diff --git a/drivers/usb/gadget/u_serial.c b/drivers/usb/gadget/u_serial.c
index 1662d83..ea360fd 100644
--- a/drivers/usb/gadget/u_serial.c
+++ b/drivers/usb/gadget/u_serial.c
@@ -36,11 +36,12 @@
  * "serial port" functionality through the USB gadget stack.  Each such
  * port is exposed through a /dev/ttyGS* node.
  *
- * After initialization (gserial_setup), these TTY port devices stay
- * available until they are removed (gserial_cleanup).  Each one may be
- * connected to a USB function (gserial_connect), or disconnected (with
- * gserial_disconnect) when the USB host issues a config change event.
- * Data can only flow when the port is connected to the host.
+ * After this module has been loaded, the individual TTY port can be requested
+ * (gserial_alloc_line()) and it will stay available until they are removed
+ * (gserial_free_line()). Each one may be connected to a USB function
+ * (gserial_connect), or disconnected (with gserial_disconnect) when the USB
+ * host issues a config change event. Data can only flow when the port is
+ * connected to the host.
  *
  * A given TTY port can be made available in multiple configurations.
  * For example, each one might expose a ttyGS0 node which provides a
@@ -120,13 +121,10 @@
 	struct usb_cdc_line_coding port_line_coding;	/* 8-N-1 etc */
 };
 
-/* increase N_PORTS if you need more */
-#define N_PORTS		4
 static struct portmaster {
 	struct mutex	lock;			/* protect open/close */
 	struct gs_port	*port;
-} ports[N_PORTS];
-static unsigned	n_ports;
+} ports[MAX_U_SERIAL_PORTS];
 
 #define GS_CLOSE_TIMEOUT		15		/* seconds */
 
@@ -1033,10 +1031,19 @@
 gs_port_alloc(unsigned port_num, struct usb_cdc_line_coding *coding)
 {
 	struct gs_port	*port;
+	int		ret = 0;
+
+	mutex_lock(&ports[port_num].lock);
+	if (ports[port_num].port) {
+		ret = -EBUSY;
+		goto out;
+	}
 
 	port = kzalloc(sizeof(struct gs_port), GFP_KERNEL);
-	if (port == NULL)
-		return -ENOMEM;
+	if (port == NULL) {
+		ret = -ENOMEM;
+		goto out;
+	}
 
 	tty_port_init(&port->port);
 	spin_lock_init(&port->port_lock);
@@ -1052,115 +1059,11 @@
 	port->port_line_coding = *coding;
 
 	ports[port_num].port = port;
-
-	return 0;
+out:
+	mutex_unlock(&ports[port_num].lock);
+	return ret;
 }
 
-/**
- * gserial_setup - initialize TTY driver for one or more ports
- * @g: gadget to associate with these ports
- * @count: how many ports to support
- * Context: may sleep
- *
- * The TTY stack needs to know in advance how many devices it should
- * plan to manage.  Use this call to set up the ports you will be
- * exporting through USB.  Later, connect them to functions based
- * on what configuration is activated by the USB host; and disconnect
- * them as appropriate.
- *
- * An example would be a two-configuration device in which both
- * configurations expose port 0, but through different functions.
- * One configuration could even expose port 1 while the other
- * one doesn't.
- *
- * Returns negative errno or zero.
- */
-int gserial_setup(struct usb_gadget *g, unsigned count)
-{
-	unsigned			i;
-	struct usb_cdc_line_coding	coding;
-	int				status;
-
-	if (count == 0 || count > N_PORTS)
-		return -EINVAL;
-
-	if (gs_tty_driver)
-		return -EBUSY;
-
-	gs_tty_driver = alloc_tty_driver(count);
-	if (!gs_tty_driver)
-		return -ENOMEM;
-
-	gs_tty_driver->driver_name = "g_serial";
-	gs_tty_driver->name = PREFIX;
-	/* uses dynamically assigned dev_t values */
-
-	gs_tty_driver->type = TTY_DRIVER_TYPE_SERIAL;
-	gs_tty_driver->subtype = SERIAL_TYPE_NORMAL;
-	gs_tty_driver->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
-	gs_tty_driver->init_termios = tty_std_termios;
-
-	/* 9600-8-N-1 ... matches defaults expected by "usbser.sys" on
-	 * MS-Windows.  Otherwise, most of these flags shouldn't affect
-	 * anything unless we were to actually hook up to a serial line.
-	 */
-	gs_tty_driver->init_termios.c_cflag =
-			B9600 | CS8 | CREAD | HUPCL | CLOCAL;
-	gs_tty_driver->init_termios.c_ispeed = 9600;
-	gs_tty_driver->init_termios.c_ospeed = 9600;
-
-	coding.dwDTERate = cpu_to_le32(9600);
-	coding.bCharFormat = 8;
-	coding.bParityType = USB_CDC_NO_PARITY;
-	coding.bDataBits = USB_CDC_1_STOP_BITS;
-
-	tty_set_operations(gs_tty_driver, &gs_tty_ops);
-
-	/* make devices be openable */
-	for (i = 0; i < count; i++) {
-		mutex_init(&ports[i].lock);
-		status = gs_port_alloc(i, &coding);
-		if (status) {
-			count = i;
-			goto fail;
-		}
-	}
-	n_ports = count;
-
-	/* export the driver ... */
-	status = tty_register_driver(gs_tty_driver);
-	if (status) {
-		pr_err("%s: cannot register, err %d\n",
-				__func__, status);
-		goto fail;
-	}
-
-	/* ... and sysfs class devices, so mdev/udev make /dev/ttyGS* */
-	for (i = 0; i < count; i++) {
-		struct device	*tty_dev;
-
-		tty_dev = tty_port_register_device(&ports[i].port->port,
-				gs_tty_driver, i, &g->dev);
-		if (IS_ERR(tty_dev))
-			pr_warning("%s: no classdev for port %d, err %ld\n",
-				__func__, i, PTR_ERR(tty_dev));
-	}
-
-	pr_debug("%s: registered %d ttyGS* device%s\n", __func__,
-			count, (count == 1) ? "" : "s");
-
-	return status;
-fail:
-	while (count--) {
-		tty_port_destroy(&ports[count].port->port);
-		kfree(ports[count].port);
-	}
-	put_tty_driver(gs_tty_driver);
-	gs_tty_driver = NULL;
-	return status;
-}
-EXPORT_SYMBOL_GPL(gserial_setup);
-
 static int gs_closed(struct gs_port *port)
 {
 	int cond;
@@ -1171,56 +1074,77 @@
 	return cond;
 }
 
-/**
- * gserial_cleanup - remove TTY-over-USB driver and devices
- * Context: may sleep
- *
- * This is called to free all resources allocated by @gserial_setup().
- * Accordingly, it may need to wait until some open /dev/ files have
- * closed.
- *
- * The caller must have issued @gserial_disconnect() for any ports
- * that had previously been connected, so that there is never any
- * I/O pending when it's called.
- */
-void gserial_cleanup(void)
+static void gserial_free_port(struct gs_port *port)
 {
-	unsigned	i;
+	tasklet_kill(&port->push);
+	/* wait for old opens to finish */
+	wait_event(port->port.close_wait, gs_closed(port));
+	WARN_ON(port->port_usb != NULL);
+	tty_port_destroy(&port->port);
+	kfree(port);
+}
+
+void gserial_free_line(unsigned char port_num)
+{
 	struct gs_port	*port;
 
-	if (!gs_tty_driver)
+	mutex_lock(&ports[port_num].lock);
+	if (WARN_ON(!ports[port_num].port)) {
+		mutex_unlock(&ports[port_num].lock);
 		return;
-
-	/* start sysfs and /dev/ttyGS* node removal */
-	for (i = 0; i < n_ports; i++)
-		tty_unregister_device(gs_tty_driver, i);
-
-	for (i = 0; i < n_ports; i++) {
-		/* prevent new opens */
-		mutex_lock(&ports[i].lock);
-		port = ports[i].port;
-		ports[i].port = NULL;
-		mutex_unlock(&ports[i].lock);
-
-		tasklet_kill(&port->push);
-
-		/* wait for old opens to finish */
-		wait_event(port->port.close_wait, gs_closed(port));
-
-		WARN_ON(port->port_usb != NULL);
-
-		tty_port_destroy(&port->port);
-		kfree(port);
 	}
-	n_ports = 0;
+	port = ports[port_num].port;
+	ports[port_num].port = NULL;
+	mutex_unlock(&ports[port_num].lock);
 
-	tty_unregister_driver(gs_tty_driver);
-	put_tty_driver(gs_tty_driver);
-	gs_tty_driver = NULL;
-
-	pr_debug("%s: cleaned up ttyGS* support\n", __func__);
+	gserial_free_port(port);
+	tty_unregister_device(gs_tty_driver, port_num);
 }
-EXPORT_SYMBOL_GPL(gserial_cleanup);
+EXPORT_SYMBOL_GPL(gserial_free_line);
+
+int gserial_alloc_line(unsigned char *line_num)
+{
+	struct usb_cdc_line_coding	coding;
+	struct device			*tty_dev;
+	int				ret;
+	int				port_num;
+
+	coding.dwDTERate = cpu_to_le32(9600);
+	coding.bCharFormat = 8;
+	coding.bParityType = USB_CDC_NO_PARITY;
+	coding.bDataBits = USB_CDC_1_STOP_BITS;
+
+	for (port_num = 0; port_num < MAX_U_SERIAL_PORTS; port_num++) {
+		ret = gs_port_alloc(port_num, &coding);
+		if (ret == -EBUSY)
+			continue;
+		if (ret)
+			return ret;
+		break;
+	}
+	if (ret)
+		return ret;
+
+	/* ... and sysfs class devices, so mdev/udev make /dev/ttyGS* */
+
+	tty_dev = tty_port_register_device(&ports[port_num].port->port,
+			gs_tty_driver, port_num, NULL);
+	if (IS_ERR(tty_dev)) {
+		struct gs_port	*port;
+		pr_err("%s: failed to register tty for port %d, err %ld\n",
+				__func__, port_num, PTR_ERR(tty_dev));
+
+		ret = PTR_ERR(tty_dev);
+		port = ports[port_num].port;
+		ports[port_num].port = NULL;
+		gserial_free_port(port);
+		goto err;
+	}
+	*line_num = port_num;
+err:
+	return ret;
+}
+EXPORT_SYMBOL_GPL(gserial_alloc_line);
 
 /**
  * gserial_connect - notify TTY I/O glue that USB link is active
@@ -1237,8 +1161,8 @@
  *
  * Caller needs to have set up the endpoints and USB function in @dev
  * before calling this, as well as the appropriate (speed-specific)
- * endpoint descriptors, and also have set up the TTY driver by calling
- * @gserial_setup().
+ * endpoint descriptors, and also have allocate @port_num by calling
+ * @gserial_alloc_line().
  *
  * Returns negative errno or zero.
  * On success, ep->driver_data will be overwritten.
@@ -1249,11 +1173,18 @@
 	unsigned long	flags;
 	int		status;
 
-	if (!gs_tty_driver || port_num >= n_ports)
+	if (port_num >= MAX_U_SERIAL_PORTS)
 		return -ENXIO;
 
-	/* we "know" gserial_cleanup() hasn't been called */
 	port = ports[port_num].port;
+	if (!port) {
+		pr_err("serial line %d not allocated.\n", port_num);
+		return -EINVAL;
+	}
+	if (port->port_usb) {
+		pr_err("serial line %d is in use.\n", port_num);
+		return -EBUSY;
+	}
 
 	/* activate the endpoints */
 	status = usb_ep_enable(gser->in);
@@ -1357,4 +1288,63 @@
 }
 EXPORT_SYMBOL_GPL(gserial_disconnect);
 
+int userial_init(void)
+{
+	unsigned			i;
+	int				status;
+
+	gs_tty_driver = alloc_tty_driver(MAX_U_SERIAL_PORTS);
+	if (!gs_tty_driver)
+		return -ENOMEM;
+
+	gs_tty_driver->driver_name = "g_serial";
+	gs_tty_driver->name = PREFIX;
+	/* uses dynamically assigned dev_t values */
+
+	gs_tty_driver->type = TTY_DRIVER_TYPE_SERIAL;
+	gs_tty_driver->subtype = SERIAL_TYPE_NORMAL;
+	gs_tty_driver->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
+	gs_tty_driver->init_termios = tty_std_termios;
+
+	/* 9600-8-N-1 ... matches defaults expected by "usbser.sys" on
+	 * MS-Windows.  Otherwise, most of these flags shouldn't affect
+	 * anything unless we were to actually hook up to a serial line.
+	 */
+	gs_tty_driver->init_termios.c_cflag =
+			B9600 | CS8 | CREAD | HUPCL | CLOCAL;
+	gs_tty_driver->init_termios.c_ispeed = 9600;
+	gs_tty_driver->init_termios.c_ospeed = 9600;
+
+	tty_set_operations(gs_tty_driver, &gs_tty_ops);
+	for (i = 0; i < MAX_U_SERIAL_PORTS; i++)
+		mutex_init(&ports[i].lock);
+
+	/* export the driver ... */
+	status = tty_register_driver(gs_tty_driver);
+	if (status) {
+		pr_err("%s: cannot register, err %d\n",
+				__func__, status);
+		goto fail;
+	}
+
+	pr_debug("%s: registered %d ttyGS* device%s\n", __func__,
+			MAX_U_SERIAL_PORTS,
+			(MAX_U_SERIAL_PORTS == 1) ? "" : "s");
+
+	return status;
+fail:
+	put_tty_driver(gs_tty_driver);
+	gs_tty_driver = NULL;
+	return status;
+}
+module_init(userial_init);
+
+static void userial_cleanup(void)
+{
+	tty_unregister_driver(gs_tty_driver);
+	put_tty_driver(gs_tty_driver);
+	gs_tty_driver = NULL;
+}
+module_exit(userial_cleanup);
+
 MODULE_LICENSE("GPL");